1. Field of the Invention
The invention relates generally to the field of lithographic processing techniques and more specifically to techniques using lasers for fabrication of electronic devices using lithography. The inventive laser techniques are particularly useful in fabricating such components as thin-film magnetic read/write heads for magnetic storage devices for digital data processing systems.
2. Description of the Prior Art
Microlithographic techniques have been advantageously used for a number of years in the fabrication of a number of types of electronic equipment. Such techniques are used, for example, in semiconductor processing, and more recently have been applied to the manufacture of read/write heads used in disk mass data storage units.
In microlithograph fabrication of electronic components, a workpiece, such as a substrate in the case of semiconductor processing, is first formed. Lithographic techniques are then used to form the various circuit and other features in the workpiece. In such techniques, various layers of material are deposited and the features are outlined therein by means of a photoresistive material ("photoresist") that is applied and patterned in a well-known manner. After the photoresist is patterned, portions of the workpiece or selected layers under the regions not covered by the masks are removed by chemical or ion beam etching. This procedure is typically repeated a number of times to form the final device.
A number of problems arise, however, in both chemical and ion beam etching. In chemical etching, the chemicals that are used to perform the etch not only remove the unprotected material from the unmasked areas, they also tend to undercut, at least slightly, the portions of the workpiece directly under the edges of the masked areas. This occurs because, as the etching chemicals remove the unmasked material, the sidewalls of the regions directly under the masks are exposed to the chemicals, which also are etched. This undercutting limits the size of the features that can be formed in the device. In particular, in designing a device, the designer must take into account the degree of undercutting that would be expected during device fabrication when he is determining how close features can be and the minimum widths of the features.
With ion beam etching, the ion beam which performs the etch is unidirectional. Accordingly, if the ion beam is directed perpendicular to the surface of the workpiece, undercutting does not occur. However, current ion beam etching techniques use a broad ion beam which is applied to the entire workpiece, rather than to a specific portion of the workpiece. As a result, the ion beam not only removes material that is not masked, it also cuts into at least the masking material itself. Accordingly, care must be taken to ensure that the masks are thick enough so that all of the unmasked material that is to be removed is in fact removed before the mask itself is completely etched away. The mask cannot be arbitrarily thin; it must be at least thick enough so that it is not etched away before the portions of the underlying layer to be etched have been etched to the required depth. Furthermore, if the mask is too thick, it will limit the minimum feature size on the workpiece.
Another problem with ion beam etching techniques is that they use energetic particles, such as atoms or ions which are applied to the entire workpiece. When the entire workpiece is so exposed to the energetic particles, it experiences a temperature increase and heat build-up which is undesirable for such devices as the magnetic read/write heads. Furthermore, with ion beam etching, often some small amount of the material initially removed from the workpiece is redeposited elsewhere on the workpiece, which can limit the feature resolution size possible with the technique, and can also interfere with proper operation of the device in some circumstances.
Heretofore, lasers have also been used to etch certain difficult to etch workpiece materials such as ceramics and certain polymers, and also in trimming such circuit elements as thin film resistors. In the existing laser techniques, the laser beam is focused to a tiny spot, which is directed onto the surface of a workpiece. The spot is moved over the surface of the workpiece to remove the unwanted material. This eliminates the need for masking, but it has at least several drawbacks. For example, in laser etching the size of the spot is a lower bound on the size of the features that can be formed in the workpiece, and so for a very small or arbitrarily-shaped feature sophisticated optical elements would be needed. Furthermore, since in the conventional laser technique only one feature is formed at a time, more time would be required than if the laser could operate on the entire surface of the workpiece at one time.
With all three techniques, it is also difficult, once etching begins, to stop the etch to ensure that recesses are formed which have predetermined depths that are fairly precisely defined. The depth of an etched recess varies not only with the time the etch is applied, but also with the characteristics of the materials being etched, and as between various production runs even of nominally the same materials, variations in the materials will result in variations in the depths of the recesses.